Acquiring high resolution digital image data from a scanner is traditionally done in a multiple step process. Usually a low resolution image is scanned, on which cropping, rotation, and other image processing operations are performed. Once the operator is pleased with the result on the low resolution image, a final image is scanned at higher resolution. The image processing steps performed on the low resolution image are automatically applied to the high resolution image during or after it is scanned.
The high resolution image may be scanned directly to disk, or it may appear in the operators window. Regardless of the output location, the high resolution image usually must be checked for image quality, since there are details in the high resolution image that cannot be seen in the low resolution version, and some image processing operations are resolution dependent, like descreening and unsharp masking. These operations cannot be accurately previewed on the low resolution image. A sample of the image may be scanned at high resolution, before scanning the entire image at high resolution, but this can be very time consuming relative to scanning the whole image with the hope that the quality will be good enough. The final quality check requires the operator to wait while the relatively large high resolution image is scanned, processed and displayed on his screen. Or, the operator must reload the final image at a later time.
Viewing these large images usually involves examining a scaled down version of the image, similar to the low resolution image, and selecting a portion of the image to view at full resolution. The scaled down version of the image is either made in advance and saved on disk, or created on the fly as the image is loaded from disk. These steps consume time and memory.